PartA: What volume of 10.0M NaOH is needed to prepare a buffer with a pH of 7.79 using 31.52 g of TrisHCl?

PartA: What volume of 10.0M NaOH is needed to prepare a buffer with a pH of 7.79 using 31.52 g of TrisHCl? TrisHCl is a weak base and the molecular weight is 157.67 g/mol. I found the solution, it is 6.67 milliliters.
Part B: "The buffer from Part A is diluted to 1.00 L. To half of it (500.mL), you add 0.0150 mol of hydrogen ions without changing the volume. What is the resulting pH? pKb for the base= 5.91"
Part C
What additional volume of 10.0 would be needed to exhaust the remaining capacity of the buffer after the reaction described in Part B?
Express your answer in milliliters using two significant figures.
JUST RESPONSE TO PART C ONLY!
thanks!